Blowout preventers are used on wells to control the pressure which may build within the well. They have been used on wells to close on dual tubing strings. It is desirable that when running or pulling such strings that they be supported by the blowout preventer rams. Normal support of a tubing string by a blowout preventer is accomplished by resting the joint enlargement on the rams. With dual strings in more recent wells which are much deeper, such support of both strings on the rams is not possible because the joints are normally vertically staggered and the length of the strings are such that both would not be supported adequately with only one resting on the rams. Additionally, tubing strings have safety valves installed therein and require the running of their control lines, often in encapsulated form along the exterior of the strings. Supporting the dual strings with their encapsulated control lines on a blowout preventer has not been possible with existing structures.
One prior blowout preventer structure was suitable for handling dual strings. It included an upper set of rams which sealed on the dual strings after they had been properly oriented by the lower set of rams. This structure is shown in U.S. Pat. No. 4,215,747. Another prior structure includes shear rams in an upper preventer and slip bowl rams in the lower preventer as shown in U.S. Pat. No. 4,043,389.
A blowout preventer structure shown in U.S. Pat. No. 4,057,887 includes upper and lower rams for a single string which has its shoulder supported on the lower ram, the upper and lower rams provide sealing on the string and intermediate rams are used for unthreading the string at the joint resting on the lower ram.
U.S. Pat. Nos. 2,746,710, 2,855,172, 2,947,508 and 4,229,012 all disclose blowout preventer structures in which the packing includes a series of inserts which support the packing material and which can move inwardly in varying degrees to accommodate the shape of the string on which the rams close. None of these structures are suitable for supporting dual strings and their encapsulated control lines and sealing about the dual strings and the control line.